91 f-150 won't start
When you first turn the key on, the ECA (computer) provides the ground for the fuel pump relay to run for 1-2 seconds. Unless it sees an RPM signal the fuel pump should stop. It could be the fuel pump relay is sticking or the computer is still providing the ground , which it should not. Try removing the fuel pump relay and see if the fuel pump stops, then try reinstalling the relay . If it doesn't run anymore, the relay is probably sticking closed. If it continues to run , need to confirm the fuel pump relay is still getting the ground whether from the computer or some other way. Check the diagnostic plug for corrosion because there is a terminal in that plug that when grounded with the key on will cause the fuel pump to run.
Great info. Thanks for sharing. Its really helpful !!
Senior Member
Joined: May 2011
Posts: 717
From: Colorado, near Denver
Ive seen it before. These processors were rated to last about 10000 hrs from new. That around 10 years of age at about 10000miles/year. Ive never seen a problem with the input/output buffers or even the actual processor.
Where these pcm's broke down was in the power section; the voltage dividers/regulators were the problem.
Glad you got it done!
Where these pcm's broke down was in the power section; the voltage dividers/regulators were the problem.
Glad you got it done!
Junior Member
Joined: Oct 2021
Posts: 1
Where was the ecm located?
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